Cosmologies from higher-order string corrections

Abstract

We study cosmologies based on low-energy effective string theory with higher-order string corrections to a tree-level action and with a modulus scalar field (dilaton or compactification modulus). In the presence of such corrections it is possible to construct nonsingular cosmological solutions in the context of Pre-Big-Bang and Ekpyrotic universes. We review the construction of nonsingular bouncing solutions and resulting density perturbations in Pre-Big-Bang and Ekpyrotic models. We also discuss the effect of higher-order string corrections on dark energy universe and show several interesting possibilities of the avoidance of future singularities.

15 pages, 2 figures, References are added, plenary talk at Pomeranian Workshop in Fundamental Cosmology (COSMOFUN 05), Pobierowo, Poland, 1-6 September 2005

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